Electronic apparatuses including a portable telephone and a notebook. computer have better functions and cover a broader spectrum, and an EL element and a lighting unit that are used in these apparatuses is accordingly demanded to have various functions and lighting different from those for stationary apparatuses have been accordingly demanded.
A conventional EL element and a lighting unit including the EL element will be described with reference to FIGS. 6 and 7.
FIG. 6 is a sectional view of the conventional EL element. Light-transmitting substrate 1 formed of film has plural holes 1A or notches. Light-transmitting electrode layer 2 of, for example, indium tin oxide, is formed over the whole bottom surface of substrate 1 by sputtering, a method using electron beam or the like.
Luminescent layer 3 of synthetic resin containing light-emitting material, such as zinc sulfide, dispersed therein, dielectric layer 4 of synthetic resin including barium titanate dispersed therein, and back electrode layer 5 of resin including silver or carbon are laid over electrode layer 2 by printing.
Luminescent layer 3, dielectric layer 4, and back electrode layer 5 are covered with insulating layer 6 of epoxy resin or polyester resin. Electrodes (not shown) are connected to light-transmitting electrode layer 2 and back electrode layer 5, respectively, and extend sideward. Thus, EL element 10 is obtained.
FIG. 7 is a sectional view of the lighting unit including EL element 10. Push button 11 made of insulating resin includes, at its top surface, display part 11A which is, for example, semitransparent or milk-white and is exposed in the form of, for example, a letter, a mark, or a design. Switch contact 12 is provided below push button 11. In the switch contact, wiring board 13 and flexible insulating film 14 are put together to face each other across insulating spacers 15 each having both surfaces coated with adhesive. Switch contact 12 is configured as a membrane switch including plural fixed contacts 13A on a top surface of wiring board 13 and plural movable contacts 14A on a bottom surface of insulating film 14, and contacts 13A and 14A face each other at a predetermined space.
EL element 10 having the above structure is disposed on a top surface of switch contact 12 and has hole 1A through which push part 11B projects downward from push button 11 or has a notch for positioning the element. Case 16 made of insulating resin covers these elements and has, at its top side, a hole through which push button 11 projects vertically movably. This arrangement provides a lighting unit.
When specified push button 11 is pressed downward, insulating film 14 of the above-described switch is pressed with push part 11B and sags, thereby corresponding movable contact 14A on the bottom surface of film 14 contacts with corresponding fixed contact 13A on the top surface of wiring board 13. This allows switch contact 12 to establish electrical connection and disconnection.
Upon a voltage being applied between light-transmitting electrode layer 2 and back electrode layer 5 of EL element 10 via the electrodes, luminescent layer 3 between layers 2 and 5 emits light. Plural push buttons 11 illuminates from behind with the light, which thus helps identification of buttons 11 even in dark.
Luminescent layer 3, dielectric layer 4, back electrode layer 5, and insulating layer 6 are formed over a large film having light-transmitting electrode layer 2 formed on its whole surface, and subsequently, a resulting element is divided into discrete conventional EL elements 10 each having a predetermined shape. While luminescent layer 3, dielectric layer 4, and back electrode layer 5 are covered with insulating layer 6, light-transmitting electrode layer 2 has an exposed end.
In cases that EL element 10 is used in the lighting unit, water, upon splashing on push button 11 or case 16, enters through push part 11B of button 11 or through the hole in the top side of case 16 and wets an outer periphery of EL element 10 or the end of light-transmitting electrode layer 2 at each hole 1A. This causes EL element 10 to have degraded insulation and reduced brightness.